1. Field of the Invention
This invention is in the field of producing copper platforms on integrated circuits involving a combination of sputtering and electrolytic deposition.
2. Description of the Prior Art
It is well known to apply integrated circuits to a silicon wafer. These integrated circuits have terminal points or sites for electrical contacting. These contact sites are usually composed of aluminum. They are specifically suited for wire bonding techniques.
Other connecting techniques used with integrated circuits such, for example, as soldering, require platforms for the contacting of the contact sites to the integrated circuit. These platforms must be highly solderable.
For producing the platforms, the contact sites are made of aluminum. The semiconductor wafer which is passivated with a protective nitride is first activated in a wet chemical process and is then vapor deposited with, for example, a 0.2 micron thick titanium layer and, for example, a 2 to 3 micron thick copper layer. This is followed by a tempering process of the wafer as required. Following this, there is a structuring of the contact sites by means of the conventional photo technique which is followed by the platform build-up in an electrolytic bath. After the electrolytic platform build-up, the photoresist layer is delaminated and a thin copper layer as well as the titanium layer are removed in corresponding etching agents. After an activation of the copper platforms, they are metallized in an electroless nickel or gold bath. In order to reduce the disturbing photoelectric effects at the pn/np junctions, the electroless metallization is carried out in a darkened room. To prevent a destruction of the integrated circuits on the wafer, the exposure times in the electroless baths are strictly limited.